1. Technical Field
The present disclosure generally relates to near-field communication systems and, more specifically, to the estimation of the expected power consumption of an electromagnetic transponder within the range of a field generation terminal.
2. Discussion of the Related Art
More and more portable devices (Smartphones, touch pads, etc.) are equipped with near field communication (NFC) devices.
Most often, such portable devices are capable of operating in two modes, respectively called card mode and reader mode. In card mode, the device operates as a contactless chip card to communicate with a near field communication terminal (for example, another mobile device operating in reader mode). In reader mode, the device operates as a terminal and is capable of reading contactless cards (or another device operating in card mode) like an electromagnetic transponder reader.
Electromagnetic transponder systems used in near field communications are now well known. Their operation is based on the transmission of a radio frequency radiation by the terminal or reader to communicate with, and possibly to remotely supply, a transponder present in the field of the terminal. The transponder, when it is within the range of the terminal, detects this field and communicates by modulating the load that it forms on this field. A transponder is within the range when it is capable of exploiting the field, and in particular of extracting from this field enough power for the operation of the circuits that it comprises.
The terminal and the transponder are generally tuned to a same frequency.
When the device operates in reader mode, it should most often remotely supply the transponder which is within its range and with which it wishes to communicate. Now, there are different natures of transponders, ranging from simple passive electronic tags to more complex transponders equipped with microprocessors. Further, according to the function performed by a transponder, its consumption varies.
For economical reasons (be the device operating in reader mode powered by a battery or directly by the electric power supply system), the power consumption of the readers is desired to be optimized.
It would thus be desirable to be able to adapt the power of the electromagnetic field generated by the terminal according to the expected consumption of the transponder present in front of it.
Complex systems which estimate the coupling between the oscillating circuits of the reader and of the card to adjust the power of a transmit amplifier on the reader side are now known. However, the implementation of such techniques requires multiple measurements and calculations and, most often, a communication between the two devices.